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    <title>Document</title>
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    <script>
        let arr = [1, 2, 3, 4, 5, 4, 3, 2, 1];

        // 1. 数组去重
        let r = [...new Set(arr)];
        console.log(r)

        // 2. 交集
        let arr2 = [4, 5, 6, 4, 4];
        const r2 = [...new Set(arr)].filter(item => new Set(arr2).has(item))
        console.log(r2)

        // 3. 并集
        const union = [...new Set([...arr, ...arr2])]
        console.log(union)


        // 4. 差集
        const diff = [...new Set(arr)].filter(item => !new Set(arr2).has(item))
        console.log(diff)

    </script>
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